G4RandomTools.hh

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//
// $Id: G4RandomTools.hh 90717 2015-06-08 14:19:29Z gcosmo $
//
// 
// ---------------------------------------------------------------------------
//      GEANT 4 class header file 
// ---------------------------------------------------------------------------
// Class description:
//
// Utility functions 

// History:
//
// 07.11.08 - P.Gumplinger, based on implementation in G4OpBoundaryProcess
//
// ---------------------------------------------------------------------------

#ifndef G4RANDOMTOOLS_HH
#define G4RANDOMTOOLS_HH

#include <CLHEP/Units/PhysicalConstants.h>

#include "globals.hh"
#include "Randomize.hh"
#include "G4RandomDirection.hh"

// ---------------------------------------------------------------------------
// Returns a random lambertian unit vector
//
inline G4ThreeVector G4LambertianRand(const G4ThreeVector& normal)
{
  G4ThreeVector vect;
  G4double ndotv;
  G4int count=0;
  const G4int max_trials = 1024;

  do
  {
    ++count;
    vect = G4RandomDirection();
    ndotv = normal * vect;

    if (ndotv < 0.0)
    {
      vect = -vect;
      ndotv = -ndotv;
    }

  } while (!(G4UniformRand() < ndotv) && (count < max_trials));

  return vect;
}

// ---------------------------------------------------------------------------
// Chooses a random vector within a plane given by the unit normal
//
inline G4ThreeVector G4PlaneVectorRand(const G4ThreeVector& normal)
{
  G4ThreeVector vec1 = normal.orthogonal();
  G4ThreeVector vec2 = vec1.cross(normal);

  G4double phi = CLHEP::twopi*G4UniformRand();
  G4double cosphi = std::cos(phi);
  G4double sinphi = std::sin(phi);

  return cosphi * vec1 + sinphi * vec2;
}

#endif  /* G4RANDOMTOOLS_HH */